Mayhem is a Norwegian black metal band formed in 1984 in Oslo, regarded as one of the pioneers of the Norwegian black metal scene. Mayhem's career has been highly controversial, primarily due to their violent stage performances, the 1991 suicide of vocalist Per Yngve Ohlin ("Dead") and the 1993 murder of guitarist Øystein Aarseth ("Euronymous") by former member Varg Vikernes ("Count Grishnackh"), of Burzum.

The group released a demo and an EP that were highly influential, and amassed a loyal following through sporadic and notorious live performances, attracting further attention through their ties to the string of Norwegian church burnings and the prominent incidents of violence surrounding them. They disbanded after Aarseth's murder, shortly before the release of their debut album, De Mysteriis Dom Sathanas, regarded as a classic of the black metal genre. Surviving former members Jan Axel Blomberg ("Hellhammer"), Jørn Stubberud ("Necrobutcher") and Sven Erik Kristiansen ("Maniac") reformed two years later with Rune Eriksen ("Blasphemer") replacing Aarseth. Attila Csihar and Krister Dreyer ("Morfeus") have since replaced Kristiansen and Eriksen, respectively.

The band's music strongly influenced the black metal genre and was instrumental in moving the global black metal scene away from the prevailing trend for speed metal. Their post-Aarseth material is characterised by increased experimentation. The 2007 album, Ordo Ad Chao, received the Spellemannprisen award for best metal Album.